Our group has discovered that the respiratory inhibitor, rotenone, induced 100% mammary tumors in the albino rat. The carcinogenesis with rotenone has an extraordinary importance because: 1) Rotenone is an insecticide used world-wide. 2) Rotenone tumors are the first tumors produced with a compound with well-defined biochemical action. 3) Rotenone tumors have extense mitochondrial alterations and a morphology very similar to human female mammary tumors. We propose a biological and biochemical study of the carcinogenesis of rotenone which will include: 1. A study of the influence of the various ways of administration of rotenone and the hormonal status of the animals in the carcinogenecity of rotenone. 2. A secuential study of the biochemical characteristics of rotenone tumors with emphasis on its glycolysis and respiration. 3. A study of the mechanism of action of rotenone as a carcinogen to be performed through biochemical analysis during treatment with rotenone. 4. Analysis of rotenone content of vegetables of human use and a search for other carcinogens among respiratory inhibitors and rotenone analogous.